Method of manufacture of master pattern containing an array of dots



- Sept. 16, 1969 s, A BROWN 3,457,550

METHOD oF MANUFACTURE oF MASTER PATTERN CONTAINING AN ARRAY OF DOTS Filed Aug. 27, 1965 3 Sheets-Sheet 1 Ill F15: 3 Saas f?. .Bleah/,v

Sept. 16, 1969 s. A. BROWN 3,467,560

METHOD OF MANUFACTURE OF MASTER PATTERN CONTAININQ AN ARRAY OF DOTS 3 Sheets-Sheet 2 Filed Aug. 27, 1965 FIEI BY P

Yrom/Eys Sept. 16, 1969 s. A. BROWN 3,4%?,560

METHOD OF MANUFACTURE 0F MASTER PATTERN CONTAINING AN ARRAY OF DOTS Filed Aug. 27, 1965 5 Sheets-Sheet 5 .E12-5: E l I Vfl/a L 4/C l [LN'I UI\.

.F12-E. zo A SIMS 4 Brow rra #Me-re United States Patent O 3,467,560 METHOD OF MANUFACTURE OF MASTER PAT- TERN CONTAINING AN ARRAY OF DOTS Silas A. Brown, Lake Elmo, Minn., assigner to Buckbee- Mears Company, St. Paul, Minn., a corporation of Minnesota.

Filed Aug. 27, 1965, Ser. No. 483,195

Int. Cl. B32b 3/10 U.S. Cl. 156-6 11 Claims ABSTRACT OF THE DISCLOSURE A number of identically-dimensioned incompressible spheres are placed on a flat surface and then pushed together so that each sphere makes tangential contact with the surface and with each adjacent sphere and the entire arrangement is then encapsulated in a settable compound. At least one side of the assembly is then ground down to expose the cross section of the spheres at the desired height or thickness to produce an array of dots of uniform diameter which can then be used as a pattern master for later photographic processing.

This invention relates tothe making of a dotted 60 array pattern on a master plate. More particularly the invention relates to the manufacture of said dotted 60 array master plate for the making of color television masks (or screens) used in color television picture tubes.

In the production and manufacture of color television picture tubes, it is conventionally required to combine with the inner screen surface of the picture tube a metal mask having a plurality of small circular uniformly dis.- tributed openings therethrough. The openings in these metal masks are usually formed by a photo etching process from a position photographic plate having the desired pattern of openings thereon. Such positive photographic plate is made by taking a photographic picture of a master plate which has a dotted 60 array pattern thereon.

The openings in the picture tube masks are often required to be tapered from a smaller size on the side toward the inside of the tube to a larger size toward the outside, for example. In the process of makiing these tapered openings, two photographic plates are required in the photoetching process, one plate having the inner pattern of smaller dots thereon and the other having the outer larger dot pattern. Moreover, the center to center spacing of the dots in the two patterns must be equal, that is, the two patterns must register.

The way the dotted 60 array pattern is normally produced on the master plate is by the crossing over at 60 of photographic negatives made from a straight line ruled pattern.

It will ybe appreciated that in order to achieve any degree of accuracy with the said cross-over-ruling process, the expenditure of a large amount of time and extremely careful workmanship is required.

It is the purpose and object of this invention to provide a method of producing a dotted 60 array pattern on a master plate, useful in a photo etching process for color television masks, which eliminates the conventional crossover-ruling process.

It is another object of the invention to provide, a pattern containing an array of dots in which the size and spacing of the dots can be established easily and accurately in much less time than is required in conventional ruling methods.

It is another object of the invention to provide a pattern containing an array of circular dots, in which the size of the various dots may be varied from center throughout the area of the pattern. In this respect, it is the aim of the invention to provide an array of dots of substantially rice circular character in which the size of the dots increases or decreases gradually from the center of the array outwardly to the edges in a radial sense. Such an arrangement of the openings is required in the masking screen for a curved picture tube in which the size of the openings around the periphery of the tube are required to be smaller than those in the center.

It is yet another object of the invention to provide a pattern master and its method of production, the master having an array of substantially circular dots in which the dots are contrasting in color with their background so that the pattern may be photographed to provide the desired photo etching plate. Another object of the invention is to provide a pattern master having an array of circular openings in the surface thereof and capable of use by contact photography, as well as a method of making this master.

Still another object of the invention is to provide a pattern master useful in the production of color television tube masks having tapered openings, the master supplying both of the patterns required for such masks.

The invention is particularly useful in producing a pattern containing a 60 dot array, that is one in which the centers of the dots are located at the corners of an equilateral triangle. To make this array, a plurality of steel ball bearings of uniform predetermined size are placed on an optically flat surface, provided with a thin layer of adhesive. The balls are held in the desired pattern `by a plurality of bars having straight edges thereon in contact with the balls. Any number of`straight edges may be employed as dictated by the desired external shape of the array. The straight edge 'bars are spring 'biased toward one another and are mounted for floating movement so that the balls themselves may dictate the shape of the array. The balls will favor a hexagonal close packed array, that is one in which the 60 angle will be maintained. A second optically at plate is employed to press on the free surfaces of the balls to insure that they are all in contact with the first optically flat pate. After the adhesive which has been placed on the rst plate has dried, the second optically flat plate is removed and a quantity of settable material such as an epoxy resin is poured over the array of balls. Enough resin is poured in to cover the balls and if desired the second optically flat plate may be placed back on the free surface of the resin to provide a form or mold therefor. If this is done it is advisable to apply a mold release agent to the surface of the second optically flat plate.

After the resin has solidified, the surface of the assembly is ground down to expose cross sections of the spheres. The resin, forming a matrix for the spheres, will be ground down simultaneously and will occupy the spaces between the circles representative of the spheres. The grinding operation is continued until the desired size of dot is achieved. By grinding a truly at surface on the material, the same cross section of each of the spheres will be exposed and an array of dots of uniform diameter will be produced. If it is desired to vary the size of the dots in the array for example to produce a pattern as described above, the surface may be ground to a spherical configuration, either convex or concave depending on the desired variation in the dot size. If the end result is to be a plate or pattern with a gradually and uniformly increasing dot size considered radially from the center of the array, the surface is ground to a convex configuration, so that at the center of the array less material is removed and thus the exposed cross sections of the spheres are smaller.

The pattern as described above may be transferred by a direct photography process where the array is photographed with a camera, or a contact process may be em ployed. In the former case, the spheres are etched slightly to provide voids in the free exposed surfaces thereof and a pigment is spread on of contrasting color to the resin matrix material. The pigment will enter the voids created by the etching step and when wiped off enough of the pigment will remain in the voids to give the spheres a contrasting color. If it is desired to use a direct contact printing process, the etching acid is applied and the spheres entirely eaten away to leave spherical voids in the matrix material. It is understood that the base plate will be a transparent material and the adhesive which originally secured the balls thereto will be transparent in this instance so that light may be transmitted through the openings in the opaque resin to expose a photosensitive film or glass on the opposite side thereof. e

The invention also contemplates a master in which the balls and resin are separated from the base plate after the resin has cured and in which opposite faces of the master are ground to provide two arrays of dots in accurate registry with one another for use in making tapered openings as mentioned above.

Other objects, advantages and new features of the invention will become apparent from a reading of the following detailed description when read in conjunction with the accompanying drawings wherein- FIGURE 1 is a plan view of a jig or xture according to the invention showing the array of balls in place on the xture;

FIGURE 2 is a partial plan view of the assembly shown in FIGURE 1;

FIGURE 3 is an elevational view of an assembly according to FIGURE 1 with a cover plate in place;

FIGURE 4 is a vertical cross section through the assembly showing the resin and adhesives in place;

FIGURE 5 is a vertical cross section through the assembly during the grinding operation;

FIGURE 6 is a microscopic cross section through a portion of one of the spheres at the free surface thereof showing the result of the etching and coating operation;

FIGURE 7 is a partial showing of the exposed finished surface of the pattern after the coating operation of FIGURE 6;

FIGURE 8 is a pictorial representation of a camera apparatus for photographing the surface of the pattern;

FIGURE 9 is a cross section through a master pattern made according to an alternative form of the invention; and

FIGURE 10 is a cross section through a master pattern made according to still another alternative form of the invention.

The jig or fixture utilized in the practice of the present invention is indicated generally at 10 in FIGURE 1 in place on a base plate 11 which is part of the master pattern being made. Iig 10 has a fence 12 resting on and upstanding from the top surface 13 of plate 11. As illustrated in FIGURE 1, fence 12 is hexagonal in form, but it will be understood that the form of the fence 12 may be varied as desired. For example, the fence 12 may be triangular or rectangular as well.

The top surface 13 of plate 11 is ground to an optically flat condition, at least in the region 15 within the inner wall 16 of fence 12. Surface 13 provides a datum surface to support the spheres 18, which will form a part of the finished master, with their centers in a common horizontal plane. Spheres 18 are of equal size, at least as equal as manufacturing tolerances will allow.

In the illustrated embodiment, the spheres 18 are disposed in hexagonal close packing. In order to hold them in this condition, a plurality of rigid bars 20 are provided. Bars 20 have straight edges 21 ground thereon so as to provide uniform contact with spheres 18 along the edges.

Each of the straight edge bars 20 is supported on the fence 12 in a manner to allow free radial movement thereof. To this end each of the bars 20l has a pair of guide rods 23 extending rearwardly therefrom. Guide rods 23 pass through openings 24 in the fence 12. vOpenings 24 are bored somewhat larger than the outside diameter of the guide rods 23 so that limited pivotal movement of the bars 20 is possible to permit the bars 20 to follow and conform to the pattern dictated by the spheres.

Bars 20 are biased radially inwardly in FIGURE 1 by means of springs 25 in encircling relation thereto and disposed between the fence 12 and the bars.

It is desirable to hold the bars 20 in retracted position while certain operations are being performed. To accomplish this any desired latching means may be employed but it is preferable that the latching means not extend above the top surface of the bars 20, since that would interfere with part of operation which will appear more fully hereinafter. In the illustrated embodiment, the latching means consist of the transversely extending pin 28 on each of the rods 23. A cooperating groove or key way 29 in each of the bores 24 will permit the rod 23 to move toward the center of the array when the rods 23 are rotated to bring the pins 28 into registry therewith. To hold the rods in the retracted position, the user need only grasp the knurled portion 31 of the rods 23, withdraw the rods until the pins 28 clear the outside wall 32 of the fence 21, and then rotate the pins out of registry with the key way 29. -The pins 28 will then rest against the rear surface 32 of the fence 12 under the action of the springs 2S.

In the process as carried out in its preferred embodiment, the balls 18 are secured to the fiat surface 15 of the base 11 by means of an adhesive. The adhesive indicated at 33 in FIGURES 4 and 5 is spread on the surface 15 prior to introduction of the balls 18 thereon. After the adhesive has been spread, the spheres 18 are disposed within the boundary formed by the bars 20 and the bars 20 are then released to move radially inwardly to hold the balls in place. Next, referring to FIGURE 3, a plate 36, having an optically flat surface 37 thereon, is lowered on to the top of the balls 18 to press them into uniform contact with the surface 15. The inherent weight of plate 36 may be sufficient to accomplish this, but if desired a weight 38 may be placed on the top surface thereof.

After the adhesive has set, the plate 36 is withdrawn and a quantity of settable material such as an epoxy resin is poured over the balls 18. The resin appears at reference numeral 40 in FIGURE 4 for example. Sufficient resin is employed to cover the spheres 18 and to fill the voids between them, thus forming a matrix to support and hold the balls 18. The exposed surface of the resin 40 may be formed fiat by placing plate 36 back on top of the surface thereof. It is advisable however when doing this to coat the plate 36 with a mold release agent so that it may be easily withdrawn after the resin has set.

lUpon completion of the curing process of the resin 40, the plate 36 is withdrawn as Well as the jig 10. This then leaves the work piece consisting of the base 11, the matrix of resin 40 and the balls 18 in place thereon. The next step in the process is to grind the top surface of the resin 40 and the balls 18.

In the grinding operation, sufficient material of the matrix and of the balls is removed to provide a surface 41, see FIGURE 5, disposed in predetermined spaced relationship to the surface 15 on plate 11. The grinding may be done in any desired manner, but for illustrative purposes, a part of a grinding machine 43 has been shown in FIGURE 5 with an abrasive surface in contact with surface 41. The depth to which the grinding is carried out will control the size of the dots which will appear in the finished pattern, since the amount of area of exposed cross section of the balls 18 is a direct function of the depth of the grinding operation. The configuration of surface 41 controls the variation in size of the dots in the gressively smaller as the radial distance from the center increases. Of course, if it is desired that all of the circles be of the same area, the grinding will be flat and if it is desired to have larger dots at the periphery than in the center the surface 41 can be ground with a convex upward shape.

Balls 18 may be of any desired material, as long as the material is capable of being formed into uniformly sized spheres and possesses dimensional stability. As the process has been carried out, the balls 18 have been steel and the matrix material has been a black epoxy resin. They with these materials, the result after the grinding step is a black background with silver or metallic dots thereon. Since the pattern on the master is transferred by photographic processes, it is desirable to increase contrast between the dots and the background. In order to increase the contrast, the following steps are carried out.

The surface 41 is coated with an etching material reactive with the metal of the balls 18 but inert with respect to the matrix material. The action of the etching material creates a rough surface on the free exposed surfaces of the balls 18 because of the variations in the crystalline structure thereof. After sufficient time has passed to etch voids in the surface of the balls 18 to a depth of approximately .003 inch, the acid is neutralized and cleaned from the surface.

A pigment of contrasting color to the black epoxy of the matrix material is now painted over the surface 41. This material will enter the voids left by the etching process. After the vehicle for the contrasting pigment has dried, the surface is polished until all of the pigment has been removed from the black epoxy surface. The result is as suggested in FIGURE 6. Here the material of the metal ball as indicated at 18 and the matrix material at 40. The surface of the metal 18 is indicated as rough at 44. The pigment is illustrated as filling the voids and has been designated by reference numeral 46 and the free surface after the completion of the polishing operation is again identified at 41. The result is illustrated in FIG- URE 7 where a portion of the surface of the master has been drawn with the matrix material colored black.

The surface of the master is now adapted to be photographed to provide, for example, a negative having an array of black dots on a transparent background.

To insure that the size of the dots in the resulting negative or transparency will be equal, it is necessary to insure that the optical axis of the photographic equipment be exactly normal to the surface of the master array. A suitable apparatus for making the photographic reproduction is illustrated in FIGURE 8. The camera is indicated generally at 48 and is mounted by means of a suitable bracket 49 on an upstanding post 50 on a base 52. The base 52 is also provided with a plane surface 53 on which the plate 11 with the master array thereon may be placed to be photographed. Suitable adjusting means not shown may be employed on the base 52 in order to vary the horizontal position of the master plate 11 under the camera. This apparatus is especially necessary when a curved upper surface has been ground on the display since in this instance it is necessary that the center of the array be disposed directly on the optical axis in order to insure accurate reproduction of the dots. After the transparency has been made according to the above described process, the method is complete.

Another embodiment of the invention avoids the use of photographic equipment to obtain a finished product. This embodiment is illustrated generally in FIGURE 9 where a direct contact printing arrangement is illustrated. In this embodiment the steps of the process are substantially the same up until the etching step with the exception that a transparent base 11a is employed and the adhesive 33a in this instance is also chosen to be transparent. The epoxy resin need not be black in this instance but need only be opaque in order to accomplish the desired result.

In the etching step in the embodiment according to FIGURE 9, the etching material is allowed to be in contact with the metal of the balls 18 for a sufficient period of time to completely dissolve the metal and to leave spherical voids 54 in the material of the matrix, the effect of this being to leave a plurality of circular openings in the surface 41a of the resin 40a. The resulting master may then be placed directly on the surface of a photosensitive plate 55 and the plate exposed by transmission of light through the transparent plate 11a and the resin 33a to expose the plate.

The pattern master illustrated in FIGURE l0 provides two arrays of dots which are of different size but in which the patterns are in accurate registry. The master is useful in making plates which in turn may be used to make tapered openings in picture tube masks or the like. While the master according to this embodiment of the invention has been shown as adapted for transfer by camera photography, it will be understood that it may be adapted for direct contact photography as well.

The master of FIGURE 10 is made in much the same way as the FIGURE 9 embodiment. The differences in the basic process are that dark colored or black resin is used throughout and that a mold release agent is employed on the optically flat base plate so that the balls 18 and their resin matrix may be separated therefrom. Both sides of the master are then ground to provide surfaces indicated in FIGURE l0 as 41b and 41C, the depth of grinding on each side being selected such that the desired different sizes of the dots in the two patterns are established.

After completion of the grinding operation, the balls in the FIGURE l0 embodiment may be pigmented as described above or they may be entirely etched out of the matrix to form a master similar to that of FIGURE 9. It will be apparent that each side 41b and 41e will contain a dot array and that since the corresponding dots in each array are formed from the same parent ball, these two arrays will necessarily be in perfect registry with each other.

It should be apparent from a reading of the above description that a unique process of making a master pattern containing an array of circular dots has been described which fully meets the objects of the inventions set forth above, which is simple to perform and which is extremely accurate in the results which it produces. The master itself is unique in that its structure provides the extremely accurate spacing and dot size which are required in the later utilization of the pattern. The center to center spacing of the dots is accurately determined by choosing the correct size of the starting balls 18 and the size of the dots in the resulting array is accurately established, as described above, by accurate grinding of the surface of the plate.

It should further be apparent that the master produced by the invention is of a permanent nature, less subject, if at all, to breakage, deterioration, or accidental disfguration or defacing.

The master further is unique in that photographic negatives or positives made thereof, either by camera or by contact, will have less tendency to show so called moire areas or spots thereon.

I claim: 1. A method of making a pattern containing an array of substantially circular dots, comprising the steps of:

disposing a plurality of spheres of equal diameter over a plane surface with each sphere making point contact with said surface and with each adjacent sphere;

flowing setta'ble material over said spheres while in said arrangement to form a matrix;

curing said settable material while maintaining the spheres in point contact with the adjacent spheres; and

grinding matrix material and sphere material away to form an exposed surface in spaced relation to said plane surface, whereby circular cross sections of said spheres will appear in said exposed surface.

2. A method as recited in claim 1 wherein said grinding step is performed in such manner that said exposed surface is planar in form and parallel to said plane surface;

whereby said circular cross sections are of equal diameter.

3. A method as recited in claim 1 wherein said grinding step is performed in such manner that said exposed surface is spherically concave upward in form, the tangent to said exposed surface at the center of the array being parallel to said plane surface;

whereby said circular cross sections decrease in diameter as the radial distance from the center of the array increases.

4. A Amethod as recited in claim 1 wherein said grinding step is performed in such manner that said exposed surface is spherically convex upward in form, the tangent to said exposed surface at the center of the array being parallel to said plane surface;

whereby said circular cross sections increase in diameter as the radial distance from the center of the array increases.

5. A method as dened in claim 1 wherein said matrix material and said spheres are of contrasting colors.

6. A method as defined in claim 1 comprising the further steps of;

applying to said exposed surface an etching lmaterial reactive with sphere material but not with matrix material;

removing said etching material from contact with said exposed surface after a predetermined time sufficient to form a plurality of voids in the exposed surfaces of said spheres;

coating said exposed surface with a pigment of a color contrasting to the color of said matrix material, whereby said pigment is caused to enter said voids, and

polishing said exposed surface to remove said pigment from said matrix material while leaving pigment in said voids, whereby the contrast between said spheres and said matrix material is enhanced.

7. A method of making a pattern containing an array of circular dots comprising the steps of;

coating a plane surface with an adhesive material;

disposing a plurality of metal spheres of equal size over said plane surface in a pattern corresponding to the desired dot pattern;

applying force simultaneously to all said spheres to insure a uniform degree of contact between said spheres and said plane surface;

pouring an opaque resin over said spheres in sufficient amount to cover said spheres;

curing said resin; and

grinding the free surface of said resin and said spheres down to a predetermined depth to expose a circular cross section of each of said spheres.

8. A method as recited in claim 7 including the further step of holding said spheres in hexagonal closest packing relation on said surface.

9. A method of making a pattern containing an array of circular dots comprising the step of;

grinding an optically flat surface on a base plate;

disposing a plurality of metal spheres of predetermined equal size on said flat surface;

applying force simultaneously to all of said spheres in a direction normal to said flat surface, to insure a uniform degree of contact between said spheres and said flat surface, and in directions parallel to said flat surface, to insure an uniform degree of contact between sa'id spheres;

removing the force normal to said flat surface;

flowing settable matrix material over said spheres in sufficient quantity to cover said spheres;

curing said matrix material;

grinding matrix material and sphere material away to provide an exposed surface in predetermined spaced relation to said flat surface, whereby cross sections of said spheres of predetermined area will appear in said exposed surface;

applying to said exposed surface an etching substance reactive with the metal of said spheres but non-reactive with said matrix material;

removing said etching substance after a time sufficient to create voids in the exposed surfaces of said spheres;

coating said exposed surface with a pigment contrasting in color to the color of said matrix material, whereby said pigment enters said voids, and

polishing said exposed surface to remove pigment from the surface of said matrix material while leaving pigment in said voids.

l0. A method of making a pattern adapted to produce an array of circular dots by direct contact printing comprising the steps of;

grinding an optically dat surface on a base member of transparent material;

coating said surface with a thin layer of adhesive;

disposing a plurality of spheres on the adhesive coatapplying force simultaneously to all of said spheres to force them into uniform contact with said adhesivecoated flat surface;

curing said adhesive and removing said force after the adhesive has set;

flowing opaque settable matrix material over said spheres in sufficient amount to cover said spheres;

`curing said matrix material;

grinding bmatrix material and sphere material away to form an exposed surface in predetermined spaced relation to said at surface, whereby circular cross sections of said spheres of predetermined area will appear in said exposed surface, and

dissolving all of said sphere material out of said matrix material whereby circular, light-transmitting openings are formed in said matrix material.

11. A method of making a pattern master containing two arrays of circular dots in registry with each other comprising;

coating an optically flat surface with a mold release agent; disposing a plurality of metal spheres of equal size on said at surface in the desired pattern, the centers of said spheres thereby occupying a common plane;

flowing settable matrix material over said spheres in suflicient quantity to cover said spheres;

curing said matrix material to form a body of matrix material with said spheres embedded therein; removing said body from said at surface; grinding matrix material and sphere material away to form a first exposed surface on said =body in predetermined spaced relation to said common plane, whereby circular cross sections of said spheres of predetermined area will appear in said first exposed surface, and p grinding matrix material and sphere material away to form a second exposed surface on said body in predetermined spaced relation to said common plane, whereby circular cross sections of said spheres of predetermined area will appear in said second exposed surface.

References Cited UNITED STATES PATENTS 3,185,555 5/1965 Granitsas 65-61 XR EARL M. BERGERT, Primary Examiner M. E. MCCAMISH, Assistant Examiner U.S. Cl. X.R. 156-154 

